Minimizing internal defects in metal castings



25, 1942- c: B. FRANCIS ETAL 2,294,167

MINIMIZING INTERNAL DEFECTS IN METAL CASTING'S Filed Aug. 9, 1940 '3 Sheets-Sheet 1 (#42455 I. P404 5. w fe. I

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?atented Aug. 25, 1942 IVHNIMIZING INTERNAL DEFECTS iiN METAL CASTINGS Charles B. Francis, Pittsburgh, and Paul B. Guyer, Clairton, Pa.

Application August 9, 1940, Serial No. ssaoza 18 Claims.

This invention relates to the casting of metals,

' but is particularly concerned with the casting of liquid steel.

The principal objects are the prevention of pipe in ingots, the prevention of porosity and of segregation in steel ingots, and the prevention of dendritic structures in large ingots and castings. The invention is particularly useful in the prevention of such internal defects in ingots andafter steels of this grade have been cast, those v changes being known in the art as mold reactions, rimming, segregation, and the coalescence and concentration of nonmetallic inclusions, the last phenomenon producing a porous condition in sections of the rolled or forged products corresponding to the central portions of the ingot.

While our invention may be applied to any steel, the grades of steels to which our invention relates particularly belong to the classes known as plain carbon and low alloy steels. These steels usually contain carbon varying from 0.02 per cent to 1.00 per cent; manganese varying from 0.02 per cent to 1.00 per cent; phosphorus varying from 0.008 per cent to 0.120 per cent; and sulphur varying from 0,010 per cent to 0.100

per cent, but may contain, also, varying per-,

centages of other elements, such as copper, nickel, and molybdenum which have a low deoxidizing' power and low percentages of deoxidizing elements, such as silicon, titanium, and

aluminum, the latter class of elements being commonly employed in the art to control chemical reactions in the mold which we control by purely physical means to produce novel types of steel differing in certain ways from steels made in accordance with the practices of the prior art.

Furthermore our invention may be applied in the casting of any metal in a mold'open at the top to permit the insertion of a solid form, such as a rod or bar, into the metal while it is still in the liquid state. However, to explain the principles, efiects, and operations involved by the process of our invention, we described, as an example of its applications, the operations and the eifects as it has been applied by us to steel ingots.

To explain fully the principles of our inven-* tion, we compare it with the operations, practices, and products of the prior art of producing steel as follows:

To produce steels of the grades similar to the grades produced by our invention, certain treatments of the steels in the furnace and in the molds immediately after casting are necessary, and by the terminology of the practices of the prior art these grades are known as killed, semikilled, rimmed and capped steels.

Referring to the drawings:

Figures 1 and 1 illustrate the usual condition of an ingot of killed steel after solidification, also the manner of freezing of the liquid steel and the usual form of the pipe in a killed ingot. As a rule, the region of greatest segregation of the elements is along the central axis below the regions of the pipe, the upper continuous portion of which is known as the primary pipe;

Figures 2 and 2 illustrate our method and the means we employ for preventing the formation of pipe, and the changes we produce in the manner of freezing and of crystallization of the liquid steel through the instrumentalitiesof our invention, which impede or prevent the formation of these injurious structural and constitutional defects known as porosity, segregation and dendritic structure, as explained in detail later herein;

Figures 3 and 3 illustrate the manner of solidification of an ingot of rimmed steel and the blowholes in the ingot after solidification has taken place; but do not indicate the central region of high segregation;

Figures 4 and 4 illustrate the manner of solidification of a capped steel and the structure of the ingot after solidification has occurred; but do not indicate the region of high segregation which is centrally located in the ingot;

Figures 5 and 5 illustrate the manner of solidification and the structure of an ingot produced by our invention; and

Figures 6 and 6 illustrate the manner in which we obtained the results, as indicated in Figures 5 and 5 To explain further the principles of our invention, its application and how it accomplishes the objects for which it is designed, we first compare our method with others designed and used heretofore to reduce the waste caused by the piping of an ingot, and with the freezing or solidification of an ingot of killed steel, in the casting of which no precautions are taken to prevent normal piping and porosity.

First, we consider the nature of the cooling and the contraction on solidification, which is the cause for the formation of pipe, as illustrated in Figures 1 and 1'. Assuming that the mold has been filled with liquid steel to the level as shown in Figure 1, solidification of the liquid steel first occurs next to the wall of the ingot and the upper surface of the stool as represented by the wall section outlined by the points a, b, c and d. Up to this stage, the solidification advances from the wall of the ingot mold toward the center of the ingot at the rate of about one inch per minute, that is, the solidified portion of the ingot is about one inch in thickness at the end of one minute, its exact thickness depending upon the temperature and composition of the liquid steel, and the thickness of the wall of the mold, and of the stool. During the first minute, the ingot remains in close contact with the mold, and a mold with a thick wall is capable of re.- moving more heat and at a faster rate than a mold with a thin wall. After the formation of the first thin wall on the *ingot, which is commonly known as the "skin of the ingot", the solidification is progressively slower, advancing at a rate varying approximately as the square root of the time, so that the total thickness of the wall is approximately 2 inches in 4 minutes, 3 inches in 9 minutes, 4 inches in 16 minutes, and so on. About 100 minutes are required for an ingot 20 x 20 inches in cross section to become completely solidified.

In a fully killed steel the top of the ingot, being in contact with the air only, also begins to freeze, but at a somewhat slower rate, the freezing starting at the wall of the ingot mold and advancing toward the center. In the so-called open and semi-killed steels this freezing is retarded somewhat by agitation of the metal caused by the evolution of gases, but in the fully killed steels, the freezing advances more rapidly,

so that the whole surface is frozen in from 1 to 3,

minutes after the mold is filled. 7

'Now, as the steel solidifies it contracts. Ordinarily, the total contraction on solidification and cooling to atmospheric temperatures is between 5 and 6 per cent of the volume of the steel in the liquid state, the exact contraction depending upon the composition and the extent of deoxidation of the steel and the temperature of the liquid above the solidification range when poured into the mold. Some of this contraction, 3 to 4 per cent, appears as a sinking of the metal, making the top surfaces of the ingot concave, and as lateral contraction from the walls of the mold.

As soon as the top is completely frozen over, however, the sinking stops, and freezing progresses downward as long as liquid metal remains beneath the frozen surface. However, this freezing does not advance far without interference-because a cavity soon begins to form beneath the frozen surface, the liquid metal deingot. In addition to these macroscopic cavities, there are smaller ones that increase the total voids to about 1.5 per cent. Larger ingots give a greater volume of pipe, whether the increase involume is obtained by. increased length or.

conversely, smaller greater cross sectional area; ingots give a smaller pipe volume. In finished and send-finished material, the small cavities ,are made visible by etching a polished surface with acids, and is commonly known as porosity. Porosity is most pronounced in semi-killed and rimming steels.

The formation of these cavities is not the only harmful results of the phenomena accompanying the solidification- Steel is an alloy made up of various .elements and compounds. In the liquid state it is capable of holding all these elements and compounds in solution, but in the solid state, and at atmospheric temperatures, it does not possess this power, and some separate as microscopic and submicroscopic segregates during the solidification and subsequent cooling. Besides, many of the additions made to deoxidize and adjust the composition of the steel react with others in the purified metal to form solid I and gaseous nonmetallic matter.

Furthermore, the elements and compounds held in solution in the liquid state freeze or solidify at difierent temperatures, so that, during the process of solidification, which takes place along lines at right angles to the surfaces of the mold and the stool by the well known dendritic type of crystallization, those components having the highest freezing point crystallize first, leaving the substances with the lowest freezing point'in the liquid state. In plain carbon fully'killed steels, for example, these low melting substances consist of the compounds of iron and carbon, and of sulphur, phosphorus,

scending to compensate for the contraction tak- I ing place in the bottom part of the ingot. The final result is a cavity or a series of cavities, called the pipe, similar to that shown in the drawing of Figure 1. By careful measurements we have found that the combined volumes of the main portions of pipe in an ingot 20"x20"x72" long and weighing approximately 4 tons, vary from 91 to 125 cubic inches, depending upon the composition of the steel, the perature, and the extent of deoxidation of the molten metal. Butin addition to these larger cavities, the opposing forces of contraction cause the formation of a great number of small cavities of varying sizes, making the total shrinkage cavity volume of an ingot of this size approxitemoxidized type of plain carbon steel of medium carbon content.

' Car- Man- Phos. Sul- Point bon ganese phorus phur Per cent Per cent Per cent Per cent 1 Directlybelowthemain .84 .52 .108 .178

ortion of the pipe. 2 T rec, inches below .78 .52 .092 .136

g a r 3 T recieetbelowpointl. .50 .48 .020 .038 4 Opposite point 1, half .51 .48 .014 .035

wday from center to e ge. I 5 Edge of ingot, opposite .52 .52 .021 .02?

point 1.

Average for the .51 .50 .022 .031

ingot.

9.75 and 1.00 per cent of the total volume .of the and manganese. The result of this natural process of cooling and crystallizing, therefore, is to cause a concentration of these low melting compounds in that portion of the central axis be-= tween the lower end of the primary pipe and the apex of the bottom pyramid formed by the ab straction of heat along lines perpendicular to the stool and the wall of themold.

This separation and concentration of heterogeneous matter in the central portion of the ingot is known as segregation, the extent of which varies with the grade of steel, the size of mold, and the temperature of the metal when it is cast. The effect upon the composition of the metal along the central axis is illustrated by the following chemical analysis of metal taken from various points corresponding to points designated as i, 2, s, Q and 5 in the diagram of Figure 1, the analyses being typical of a partly de- This change in composition of the metal at and near the central axis, changes, of course, the physical properties of the metal, the higher carbon and phosphorus, in particular, making it harder and more brittle. While-in some finished sections this area of the ingot becomes a neutral axis to stresses in service, in other products, such as flat bars, strip and plate, it may lie in the direct path of cold bending, punching, drilling, or other forming operation, when it is found not only to interfere with these operations, but to cause the section of steel either to break or exhibit other undesirable tendencies.

The combined eifects of the pipe and of this ,segregation of metallic and nonmetallic components are the direct causes of many objectionable and injurious defects in the finished steel. For example, the section of pine at A-A, Figure 1*", is always connected through blowholes with the outside air, which may seep through to oxidize the surface. Lower portions of the pipe, or

' secondary pipe, as at B, become pockets in which the low freezing nonmetallic matter may collect. The results of these natural tendencies are to cause the defects known as laminations and hard spots in plate, sheet, strip, and structural shapes. In forgings of intricate design, such as many drop forgings, they may make the steel extremely unreliable, or even unsafe, as theafiected part cannot always be retained centrally located or in a neutral axis, and if the parts are heat treated,

bodiment of our invention and the manner in which it is applied, without reference to any particular design of the simple apparatus required, as follows:

A. For each ingot to be cast and treated by thi embodiment of our invention we prepare a piece of metal, to which we apply the term insert bar to the following specifications:

Composition-Usually the same as that of the steel to be cast, but if for any special reason it is desirable to have the'central axis of the finished section differ from the rest of the section, the insert bar may be of any metal or any metallic alloy having a sufliciently high fusion temperature and of the composition desired.

Form and size of section.-To prevent piping and segregation the form of the section of the insert is preferably made to conform roughly to the section of the ingot to be cast, and the sectional area should be approximately 1.7 per cent of the cross sectional area of the ingot. However, if the latter condition is complied with the form of section may be of any design; also, a multiplicity of insert bars and forms may be used in the same ingot or casting, the insert bars being either straight bars of uniform section or tapered to a the defect may cause the piece to crack and even break, or worse still, to crack internally, making a discovery impossible by any ordinary form of inspection.

Pipe is overcome by cropping the piped top from the ingot, by the use of a hot top, the capping practice, etc. Each remedy has objectionable features as is well known.

So far as we know, segregation has been accepted as an unavoidable evil, and no effective method of preventing it has been proposed. It can be lessened through control of the size, shape and form of the ingot, the segregation and concentration of the low menting components being less in small ingots than in large ones. However, the casting of small ingots is expensive and frequently impossible, particularly if the section to be formed is large and heavy, because the metal in the ingot, after the discard, may not be sufficient to form the section in the lengths desired.

The defects known as dendritic structure, columnar structure and ingotism are due to the slow cooling of the interior of an ingot or casting, which condition is always present in ingots and castings of large cross section because of the slow transfer of heat through the thick, solidified wall portion. The effects of the extremely slow rate of cooling from ,the liquid to the solid state are to cause the crystallization to take place in a typical manner, giving a tree-like or dendritic formation prior to theformation of grains which grow to large size, these processes of solidification being in turn responsible for the highly segregated condition usually found in large ingots or castings. This large grain structure, which becomes apparent when the ingot or casting is fractured, is said to be the cause of cracks in ingots near the bottom, particularly if the ingot structure is columnar in form. The only remedy for these conditions is rapid cooling of the interior as well as the exterior portions of the ingot or casting, which is accomplished by the novel means of our invention.

We now describe the principles of the chief emsection of decreasing or increasing area from top to bottom as required to conform to tapered ingots. For ingots of square sections, we have found inserts circular in section most convenient to handle, and to give satisfactory results in practice.

Length-The length of the insert bar to be immersed in the liquid steel should be such that the bottom of the insert bar will extend to within 15 of the distance to the bottom of the ingot, and preferably to or slightly below the apex of the equilateral pyramid constructed with its, base coincident with the base of the ingot. A small additional portion is usually provided for grasping in the guide form, which portion will protrude from the end of the ingot. Also, on this portion a hole, hook or loop is formed or attached to serve as a means of supporting the insert bar while it is being lowered into the ingot and for several seconds thereafter. With these attachments welded or otherwise fastened to the top of the insert bar, .the latter may be lowered until it is flush with or slightly below or above the top surface of the ingot.

TTeatment.After it has been formed and at a convenient time before use, all oxide or scale 'machining or pickling. If the bars are free from injurious defects, they need not be machined, but may be treated as delivered from the rolling mill without first removing scale on the surface of the bars. When cleaned by pickling, the insert is preferably treated by a novel process which has been devised by us and is described below. However, we have obtained a bonding satisfactory for many grades of steel by pickling the insert bar with sulphuric acid and keeping it immersed in a dilute solution (about /2 per cent) of sulfuric or hydrochloric acid until just before it is to be used. Under some conditions, it'may be desirable to dry and warm the insert bar to between C. and 200 C. just before it is inserted into the liquid steel and to employ inserts coated with various materials, such as organic mixtures and nickel, copper and the like, which will prevent corrosion and permit close bonding of the insert bar with the steel.

Two methods of treating the bar which we have found most satisfactory are described as follows: By one method we immerse the insert bars in a fused bath, consisting of about 7 parts sodium ,carbonate and 3 parts sodium cyanide. Each bar is kept in this bath. which is heated to between 1400" F. and 1550 F. until the temperature of the bar is the same as that of the bath and for to 20 minutes longer, in orderto reduce the scale and to carburize and nitride the surface to the extent desired, the exact time also depending range of the steel. When this temperature is reached, the bar is withdrawn from the cyanide or the cyanide-carbonate mixture, and the excess salt adhering to its surface is removed, preferably shortly before the bar is to be inserted into the ingot. The excess salt may be removed by any convenient means, as by brushing. We prefer, however, to wash the insert with hot water and dry it rapidly. To facilitate and speed up the drying action, the insert may be warmed or heated to abqubt 200 F. before it is immersed into or sprayed wi the hot water.- Under these conditions the insert becomes self-drying and dries very rapidly.

By this treatment all oxides on the insert are reduced. and carbon and nitrogenare absorbed by the surface metal, thus lowering its fusion temperature. When this insert is introduced into the molten steel ingot, the fusing of the surface metal gives a perfect bond between the ingot to about 500 F., and immersed in a 5 to 10 per cent solution of sulphuric acid, after which the insert bar is' carefully inspected to make certain that all of the scale has been removed. The object of heating the insert is to prevent lnrdrogen absorption by the bars and to maintain the temperature of the acid solution between 180 F. and 210 F. and thus insure rapid pickling. After all the scale has been removed in the hot sulphuric acid bath, the insert bar is washed in a dilute solution of hydrochloric acid to' remove at least some of the adhering sulphates, which would create a high sulphur area adjacent to the insert, if allowed to remain.

In the pickling of some steels, particularly those containing much chromium, copper, molybdenum, nickel, phosphorus, silicon and the like, a coating made up of the sulphates, sulphides, the hydroxldes (or hydrated oxides) of these metals, is

developed in the pickling operation. This coating, commonly referred to as smut," isnot removed by the cyanide solutions used later, and remains to prevent a close bonding of the insert bar with the liquid steel. To remove this coating heated to between 250 F. and 750 F., preferably we immediately transfer the insert bar from the hydrochloric acid wash to a wash containing a concentrated solution of caustic soda (sodium hydroxide). We may also brush or scrub the insert with hot 2 to 15 per cent solution of caustic soda to accomplish the same object, depend-- ing upon the-compositionof the steel, and redip the bar in the dilute hydrochloric acid solution.

The hot descaled insert is then immediately dipped into a very dilute solution of sodium cyanide to remove all of the ferrous sulphate formed in the pickling operation and toneutralize any trace of free acid which may adhere to the insert. The cyanide reacts with theacid to form sodium sulphate, hydrocyanic acid and ferric ferrocyanide. The iron salts also react with the hydrocyanic acid to form iron cyanides. sulphate is very soluble and sodium cyanide is a strong reducing agent, the surface of the bar is covered with athin film of the latter as the bar is removed from the bath. This film'prevents sulling or oxidation of the surface when the'insert is exposed to the air. For this purpose cyanide is added to the bath only in sufiicient quantity to keepthe pH value of the bath between 5 and 12, the poisonous sodium cyanide being constantly consumed, this e 'inating any hazard connected with the discar this bath.

The bar is then immediately dipped nide to obtain a film of this salt upon the surface of the bar. In practice this bath contains 3 to 10 ounces of sodium cyanide per gallon, the concentration being preferably kept on the high side but short of that value which may'result in the decomposition of the cyanide at the maximum operating temperature of 150 F. to which the bath may be heated by the heat from the inserts.

The bar is then placed upon a drip table until it is dry, this drying being effected within one or two minutes due to the heat content of the bar.

The film or coating formed protects the steel from rusting for from one to several days; and

the sodium cyanide, forming a soap and fixing" the cyanide in a non-toxic nonoxidizable form, and at the same time remain mixed with the others to form an oxidized film. The excess oil is permitted to drain mind that which remains on the surface of the bar is allowed to dry. This oxidized film, together with the previously formed salt film, prevents rusting of the surface of the bars, and they may be kept for months before they are used. when the bar is inserted into an ingot the salt film forms a cyaniding fiux, which causes a perfect bonding of the inserted bar with the liquid steel.

In this special oil mixture, the oxidizable oils may be soya bean oil, turpentine or castor oil, while the nonoxidizing oil may be a slushing oil such as is used to coat steel products to protect them until used. to per cent soya bean oil, linseed oil or a mixture of the two with 5 to 15 per cent turpentine and 5 per cent castor oil, these being worked into a mixture and added to the slushing oil known commercially as Socony Vacuum No. 20

Since sodium g and removal of into is. sufficiently concentrated solution of sodium cyait is dipped into a v The best mixture consists of in the proportion of one part of the mixture to three parts of the slushing oil named.

The oil film fixes the cyanide on the surface of the bar and eliminates danger of cyanide poisoning in handling the inserts. The functioning of the coating as a whole, consisting of carbonaceous oxidized oil and sodium compounds mixed with sodium and iron cyanides, may be briefly explained as followsAs the insert bar is lowered into the metal that remains molten in the ingot, a slight rise or surface boil in the metal produces a convex meniscus at the surface of the ingot which prevents drag-in of the oxide or slag which would adhere to the insert. The heat drives off the volatile oils and causes the liquid to first solidify about the cold bar, forming a layer of metal that seals in the unvolatilized and cyanided film at the interface rises to above 2100{ F., it first-melts, then becomes semi-fluid and thereby forms a perfect bond between the two bodies of metal. Subsequently, both the carbide and the cyanide diffuse into the surrounding metal, leaving the bond at the interface of the same composition as the other portion of the metal.

ingots remains open for a considerably longer time than killed steels.

E. At the end-of a period of time varying from 0.5 minute to several minutes (according to the size of ingot or casting, type of steel; whether killed, semi-killed or open and the objects it is desired to accomplish) after the ingot mold has been filled, one end of the clean, scale-free insert bar is inserted into the open area of the top crust, and the insert bar is gradually lowered into the liquid steel, finally being guided down- 4 B. The steel may be introduced into the mold.

in the usual way, which may be either by top pouring, sometimes spoken of as teeming, or by proper height, preparations for inserting the bar I are completed. Usually a metal guide or form is first placed upon the ingot mold. This form is made to fit the top of the mold and is provided with a hole in the center to act as a guide to keep the'insert bar in a position coincident with the central axis of the ingot as the insert is lowered into the molten steel. Other devices may be used to accomplish the same object and may be necessary to conform to the top of the ingot mold and perform the required function of guiding and holding the insert bar along the central axis.

D. Ifthe bar cannot be inserted at the end of about 1 minute, or slightly longer, after a mold has-been filled with a completely killed steel, the top surface is broken and kept open during the period of waiting, with a piece of dry wood, or by a suitable mixture of substances that will act to prevent the escape of heat' and to keep the top surface fluid. For this purpose we may use a combination of methods. For example, by using a dry wood block upon the top surface of the ingot after teeming, then adding a special thermit mixture of iron oxide and aluminum as heat generating agent, followed by an insulating material, we have been able o keep the tops of fully killed steel ingots open for as long as 19 minutes, which normally solidify within 1 to 2 minutes. The surface of semi-killed and rimmed wardiy until the top of the insert is a few inches below or above the surface of the liquid steel. The insert bar is lowered at such a rate that it causes little or no rise in the surface of the liquid steel above its original level. As the insert bar is thus lowered into the liquid, the metal solidifies about it, and the contraction thus produced, plus the contraction due'to the solidification at the wall, is about equal to the liquid displacement produced by the insertion of the insert bar.

Since the density of the liquid steel is 6.88 to' 7.4 grams per cm. and the density of the cold steel insert bar is about 7.8 grams per cm}, no

veniently and most safely lowered into the liquid steel with a small wir rope extending over a pulley above the mold so that lowering can be controlled from a distance.

F. After the metal adjacent to the top of the insert bar has solidified sufficiently to form an anchorage for the latter, the guide and holding device is removed from the top of the mold, and the ingot is allowed to cool for a period somewhat shorter than usual before it is sent to the stripper, where the mold is removediii the usual manner. The ingot is then transferred to the soaking pits, where it is allowed to remain until it is of a uniform temperature throughout, and thereafter treated, rolled or forged in accordance with practice standard for the plant making the steel. The time from casting to'rolling may thus bereduced from V; to 1 hour, because the heat abstracted from the molten metal by the insert bar hastens the complete solidification of the central portion of the ingot. The heat is ab-.-

stracted in a few seconds as compared with many minutes required for the slow dissipation of heat I through the wall of the ingot.

How this solid steel insert, prepared and introduced into the molten metal in the manner and after a period of time subsequent to filling the mold, as described above, prevents segregation and the formation of pipe, becoming at the same time an inseparable part of the ingot itself, if and when it is so desired, is explained as follows:

Referring again to the drawings of Figures 2* and 2 which are diagrams for an ingot 20', ,x 20 x '10", at the end of 2% to 3 minutes after the mold has been filled, solidification of the steel from the four sides in contact with the mold, and the bottom in contact with thestool, has taken place to form the shell, outlined by the lettersE, F, G, H. At this point the total contraction of the cooling metal is approaching half the volume of the insert .bar. Then the I clean insert bar, CD, is inserted in the manner stated. and no sooner is this act performed than thereto, causing a further contraction, the total being suflicient to prevent the liquid metal from rising above its original 'top level, except possibly for a slight lifting of the frozen surfaces immediately adjacent to the sides of the insert bar. Heat transfer from the liquid steel to the insert bar now progresses in accordance with the well known laws of heat exchange between two bodies at different temperatures in contact with each other, including both heat transfer from liquid to solid and heat transfer from solid to solid.

Although the heat in the liquid steel is a regulated amount in excess of that required to raise the temperature of the insert bar to the point of incipient fusion, the insert bar does not melt entirely for two reasons. First, on account of the great difference in temperature, the initial effect after its insertion is to solidify some of the molten metal in direct contact with it, and the transfer of heat thereafter must be through this solidified shell, which constantly increases in thickness until the temperature of the insert bar, itself, approaches that of the liquid steel. Second, the area of the cross section of the insert bar is so proportioned to the sectional area of the liquid steel, that the heat given up in lowering the temperature of the liquid steel to the liquidus point is barely suflicient to raise the temperature of the insert bar and. its shell of solidified metal above the solidus point.

The size or weight of a section that will give the condition described above maybe calculated from the specific heat and the latent heat of fusion of steel. I

The specific heat of steel varies with the temperature from 0.105 cal. per gram at degrees C. to 0.185 cal. per gram at 700 C. and 0.145 cal. per gram at 1400 C. We take 0.146 as the average specific heat of solid steel. The specific heat of liquid steel near its freezing point is 0.15 cal. per gram. The latent heat of fusion of steel is 0.7 cal. per gram. Therefore the heat set free bythe solidification of 1 gram of steel is equal to the heat abstracted from 4 to 6 grams of liquid steel in cooling through 1 C.

Again, 1 gram of steel at 0 degrees C. will ab-. stract 225 cal. of heat in being heated to 1500" C., and 1 gram of steel at 100 C. above its melting range will give off 15 cal. in cooling to the liquidus and 1 gram at 100 C. above its melting range will give off 85 cal. incooling to its solidus point. Therefore, 1- gram of steel at 0 degrees C. will lower 15 grams to its liquidus point and 2 grams to its solidus point. We regulate the size of the insert or inserts relative to the amount of steel in the ingot that is molten at the time of the insertion so that the cooling effect is sufiicient,to solidify about half of the liquid steel.

Conditions within the ingot after the insertion of the insert bar are such that solidification is progressing rapidly in opposite directions as indicated by the arrows in the diagram of Figure 2. Moreover, the metal about the insert, CD, solidifies at a decreasing rate similar to the rate of the solidification advancing from the surfaces of the mold and the stool, the freezing from CD continuing until it issurrounded by a body of metal either solid or in a mushy state, as represented by the lines, I, J, K, L.

The volume of the metal thus solidified or (2642 F.), that the temperature of the liquid, steel in the mold is 1500 C. (2'732 F.) and the temperature of the bar is 50 C. (122F.). From the specific heats of iron and steel, the total heat required to raise the temperature of the insert bar from 50 C. to 1450 C. is approximately 245 calories per gram, and the total heat that must be abstracted from the liquid steel to lower its temperature from 1500" C. to 1450 C., the point of incipient fusion, is 9.2 cal. per gram. Therefore, each pound, for example, of the inert bar will bring 26.6 pounds of the liquid steel to the liquidus point, that is, the temperature at which freezing begins, or 200 cubic inches of the insert bar will lower thetemperature of 5320 cubic inches of the liquid steel to the liquidus for the steel. The steel next to the insert bar solidifies,

and since the heat of fusion is about 70 cal. per

gram, the total volume of the liquid steel lowered to the liquidus, cooled to the mushy stage, and solidified completely may be calculated. However, the metal completely solidified is usually less than that indicated by calculations using the factors stated above. This is explained by thefact that the cooling effect which causes solidification is partly offset by the execess of metal that remains liquid. Our experiments show that, after the insertion has'been made and heat trans--. fer equilibrium is again established, the total area of the section of the zone solidified by the insert bar varies between 4 and 16 times the area of the section of the insert bar, according to the type of steel, temperatures of the insert bar and of the liquid 'steel when the former is lowered into-the latter, the exact relation of the cross sectional area of the insert bar to that of the ingot and other minor factors. Among these factors may be mentioned the composition of the steel, the thickness of the mold wall and the speed at which the insert bar is lowered into the ingot.

An important factor in reducing the piping tendency of the annular liquid portion surrounding the insert island, Figures 2 and 6 is the fact that the solidified wall of the ingot contracts inwardly during the cooling of the ingot and the portion solidified about the insert first contracts I but later expands as it absorbs heat from the lowered in temperature to the mushy state can be calculated from the specific heats of steel and the heat of fusion for iron as follows:

Assume the steel begins to solidify at 1450 C.

portion of the steel remaining liquid. The result of these inward and outward movements of the shell and of the solidified core, respectively, is to compensate in part for the liquid to solid contraction of the portion that is liquid at this time.

From the explanation above and from the diagram of Figure 2 it is evident that the tendency to segregation and the formation of large grains must be and is wholly prevented, for while the steel about the insert has solidified to the boundary indicated by the lines, I, J, K, L, the solidification from the wall of the mold has also progressed in an opposite direction to the boundary indicated by the lines, 0, P,'S, T, leaving very little metal in the liquid state, and it mainly in a mushy condition not at all favorable to scaregation nor to the dendritic type of crystallization. Besides the manner in which we insert our insert bar tends to prevent segregation, for metal at the top of the ingot is solidified on the insert bar and forced towards the bottom of the ingot as the insert bar is slowly lowered. As proof of this statement, we give below analyses of complete lines across ingots solidified in accordance with our invention, each line extending from the prone to segregation.

i Position of sample Mn P S No. 7

Per Per Per Per cent cent cent cent 1 Center adjacent to insert 0.07 0.30 0.127 0.038 PointZ 0.08 0. 30 0.128 0. 039 P0lnt3 0.09 0.30 0.127 0. 037 Pointi 0.10 0. 30 0.127 0. 03:; Edge of the ingot 0.10 0.30 0.130 0.038 2 Center next to insert 0.11 0.37 0.140 0042 Midway, center and edge. 0.12 0.35 0.144 0.047 One inch from edge 0.11 0.35 0.137 0.043 3 Center, next to insert 0.10 0.35 0.130 0.041 Midway, center and edg 0.12 0.35 0.147 0.039 One inch from edge 0.12 0.34 0.133 0.045

In ingots of heats of steel of the same type and grade not treated by the process of our invention, we have found the analyses of samples taken from the same relative positions in the ingot varying as much as 4 points (0.04 per cent) in carbon, points (0.10 per cent) in manganese, 40 points (0.040 per cent) in phosphorus, and 20 points (0.020 per cent) in sulphur.

In treating fully killed steels we have also succeeded in diminishing the size of the pipe cavity and improving the internal structure of the ingot by introducing into the ingot as the steel is being teemed a proportion of solid steels, in the form of small bodies, somewhat less than the proportion required for an insert bar. These small bodies are preferably in the form of short bars or small balls, cleaned and otherwise treated as described above for the insert bars. Also, steel in the form of small bodies may be added during the teeming,

and a bar smaller than we ordinarily use, in-.

serted after the teeming, to prevent the formation of pipe.

Our invention may also be applied to the treatment of rimming steels with beneficial results, the insert bar being used to control the thickness of the rim and prevent segregation and high porosity of the central portion. This application of our invention is explained as follows:

Referring particularly to rimmed steel in the sketches of Figures 3 and 3 the operations,'

practices, and results obtained in the prior art are explained as follows:

In the basic open hearth furnace the steel is subjected to the usual purifying action of basic slag, and the carbon is worked down to the point desired in the finished steel, if this is under 0.10 per cent; but if the carbon in the finished steel is above 0.15 per cent, the carbon will be worked down to 0.08 or 0.10 per cent, this working down being accomplished with the addition of iron oxide in a suitable form to the bath; and the temperature of the bath will be raised to a level corresponding to the highest tapping temperature range, which is somewhat above theliquidus for the steel. The result of operations and additions made to the bath is to saturate the metal bath with ferrous oxide, FeO, in equilibrium with the carbon, manganese, and phosphorus remaining in the metal, and with the lime, silica, and FeO in the slag. The heat is then tapped into the ladle, and additions of carbon and manganese are made, if necessary, to adjust the composition of the steel to that desired for these elements; and alloying elements, such as copper, nickel, and molybdenum, if these are required, may be introduced while the steel is in the furnace, and other elements may be added to the metal in the ladle.

In the Bessemer process 7 and the Thomas process, the oxidizing agent used is the oxygen and the acid or basic slags produced; and the temperature is controlled through the composition of the pig iron used in the charge. The addition made to adjust the composition of the steel may be made in the furnace itself or the ladle, as described for the open hearth process. The metal, however, will contain some nitrogen and some hydrogen from the nitrogen in the air and decomposition of moisture in the blast.

In any process, certain adjustments of FeO and the temperature are necessary to obtain the reactions in the mold which produce the result desired as explained below.

When this steel is teemed into the mold, solidification begins immediately at the surface of contact with the mold and progresses toward the central axis of the ingot, as indicated by the arrows in Figure 3. This solidification, pro-- vided the steel has been properly made and its temperature properly adjusted, is accompanied by chemical and physical phenomena which result in the formation of a rim of solid, dense metal next to the mold wall and this metal is somewhat. purer than that in the interior of the ingot and, also, comparatively free from nonmetallic inclusions and cavities.

This rim of metal free from defects gives a surface also free of defects on products rolled from the ingot. On this account, rimmed steel is highly valued for the production of such articles as thin plates, sheets, and strip. These are articles which require a smooth, uniform surface free from seams or other injurious defects which are likely to become enlarged when exposed to subsequent treatments, such as pickling, that may be required to produce the finished article of commerce. 4

The phenomenon known as rimming is produced by the evolution of gases as the metal solidifies. In steel produced by the basic open hearth process this gas is evolved mainly as CO generated within the metal itself by the action of the dissolved ferrous oxide with carbon, according to the simple reaction.

Thus,

FeO+C=Fe+CO I This reaction occurs in the mold and progresses more rapidly than in the furnace or in the ladle due to the fact that the steel is no longer in contact with a highly oxidizing slag, and to the manner of freezing of the liquid metal itself. Since pure iron has a higher melting point than any of its oxides or carbides or alloys, it is the first to crystallize in the rim of metal adjacent to the wall of the mold. Hence,

the influence of the process of solidification is evolution of the gas produces an ebullient effect in the metal, which is quite apparent at the surface of the ingot. The effect of this action is to retard the solidification of the metal at the top surface of the ingot,-which becomes slightly concave due to the contraction on cooling. However, as this process advances to a certain stage, the metal at the surface either freezes or tends to freeze over and that below drops to a temperature near the solidus temperature, thus becoming very viscous. At this point, the ebullient action decreases, and the gases become trapped in the metal, forming a great number of cavities, as illustrated in Figure 3*.

. bon, phosphorous, sulphur, particularly the last two. If the per cent of each present is high, this segregation is most pronounced in the upper half of the ingot and in an annular area just within the rim of solid metal. As an illustration of this action, we give below the analyses of portions of metal taken from a cross section of an ingot corresponding to the positions a, b, c, d in Figure 3".

Position- Mn P S Per cent Per cent Per cent Per cent a 0. 04 0.30 0.060 0.022 0. 06 0. 35 0. 070 0. 035 0. 08 0. 35 0.100 0.045 0.06 0.35 0. 120 0. 040

With a very low per cent of phosphorus and sulphur their segregation is less pronounced.

In the production of capped steels the procedure up to the teeming is similar, except that the temperature may not be so high as in a rimming steel. Therefore, the steel after teeming is near the solidification temperature range and the metal tends to rise in the mold, if left open to cool normally at the top surface. However, it is the practice in making this type of steel to 4 This condition not only produces a high porosity in the central size of the ingot, -*and this solidification phenomenon produces segregation, the last very much as in the case of the rimmed steel with a similar difference in the composition of the metal, if the top portion of the ingot is compared with the metal in the bottom portion.

In order to control the evolution of gas in the rimming action of rimmed steels and particularly to check the evolution of gases in capped steels and to reduce the internal pressure set up by the continued generation of gas, it is customary to add deoxidizing agents either in the ladle or in the mold, frequently in the latter. Sodium fluoride has also been added to the ingot to btain a better rimming action and less porosity.

,For the control of rimmed steels, for example, aluminum in the form of shot is added to the steel in the ingot mold. Sometimes this aluminum is distributed from top to bottom as the ingot is poured, sometimes it is added mainly at the top. In any case, the exact amount added at any point is dimcult to control, and even when precautions are taken to distribute this aluminum uniformly the manner of solidification of the steel prevents an even distribution of the aluminum in the outer shell. The result is that different types of steel, with respect to austenitic grain size, are produced in the same ingot, one portion of the ingot being of the type known as fine grain steel, and an adjacent portion of the type known as coarse grain steel. Likewise, one portion may be of a type known as aging steel,

insert a cap on the mold to chill the top surface as soon as the steel begins to rise. The effect of this procedure is. to permit a slight rimming action to proceed at first and then to cause the top to solidify as shown by Figures 4 and 4 thus stopping ebullition of gas and creating a high pressure within the solidified shell. This pressure tends to stop the reactions which normally take place, but not entirely, so that a great many gas pockets are formed, and some of these may be nearer the surface of the outer walls of the ingot than is the case with rimmed steel. Gas cavities, however, serve as pockets for the accumulation of nonmetallic materials which lead to defects in the finished metal, particularly thin plates and sheets, which are known as blisters. The same defects occur less frequently in the rimmed steels because the pockets of nonmetallic materials are located farther beneath the surface.

Although the steel is capped, causing the top portion to solidify, the interior remains fluid for a period of minutes or hours, according to the and an adjacent portion of a type known as nonaging steel. Now, these different types of steel thus produced in the ingot through the addition of the aluminum in whole or in part to the ingot mold, persist in the products produced therefrom by the subsequent forming operations and result in a mixed structure in the finished steel itself, the different types in this mixed structure having different properties as indicated by the terms used to designate them. For example, a steel of this grade, or carbon content, may be required for carburizing purposes. The fine grain and the coarse grain type may or may not absorb carbon at the same rate, but in the subsequent heat treating operations the two types of steel have different critical rates of hardening, so that it is' carbon, and manganese, which occurs in the upper part of the ingot, is a handicap in the making of steel products of small or thin section, such as sheet and wire made by modern methods of hot rolling and cold reduction. By these methods the sheets for example, are produced in long lengths or coils requiring slabs of large size to be rolled from the ingots. Howeyer, the higher phosphorus, carbon, and manganese limit the amount of reduction in thickness that may be produced by cold rolling without annealing before further rolling can be done. For example, low phosphorus, carbon, or manganese, such as that obtained in the bottom portion of an ingot, may be cold rolled, for example, from 16 gage to 30 gage in three passes without annealing, but the top part of the ingot will require five to six passes with an intermediate annealing process to reduce the thickness of the sheet from 16 gage to 30 gage.

Thus, the effect of the insertion of the bar is to By the application of our invention we produce a rimmed ingot giving all the advantages of a rimmed steel, and at the same time prevent the segregation and the formation of internal cavities common to the rimmed or capped steel. Also, by controlling the deoxidation of the steel in the furnace by known means we are able to obtain a steel having all the advantages, and in addition a steel freer from nonmetallic matter arising from the reaction of metalloids and deoxiclizers with the FeO dissolved in the metal. Furthermore, the application of our invention makes it unnecessary to add aluminum, silicon and other deoxidizing agents to the ingot, thus reducing the cost of making these high quality steels and avoiding the defects and objectionable mixed structures obtained through the use of deoxidizing agents which are commonly added to the liquid steel in the mold. Figures and 5 show an ingot made by our invention. How we accomplish these objects is explained as follows:

Starting with the steel in the open hearth or with the steel in the ladle, if it is made by the Bessemer or the Thomas process, we reduce by known means the FeO dissolved in the steel to a minimum necessary to obtain rimming action immediately after the steel is teemed into the ingot. When the ingot mold has been filled with the liquid steel and a sufficient time has elapsed to bring the temperature to 25 to 50 F. above the solidus, this being from one to several minutes, depending upon the size of the mold and the temperature of the steel as teemed, we insert into the molten metal a specially formed and prepared bar of cold steel of the desired chemical composition, this bar being inserted so that its long axis is coincident with the long axis of the ingot, or practically so.

This bar is prepared by forming it to the desired shape and by treatment or treatments, to obtain a surface free of seams and other defects and of scale and rust by one of the methods hereinbefore described.

This bar is lowered into the molten metal at such a rate that it produces little or no change in the level of the metal in the mold.

This bar may or may not be formed at the top and the bottom to present a longitudinal section as indicated by B in Figures 6 and 6 and is of a length to extend from the top to the bottom of the steel remaining liquid at the time the cold bar is inserted. To obtain best results, this bar should conform roughly to the section of the mold in which the steel is cast, and if a multiplicity of insert bars are employed, the action of the zone solidified should conform to the shape of the mold. The cross sectional area of the bar or bars may vary from one to several per cent of the cross sectional area of the ingot itself, so that it will not be completely melted by the liquid steel. These bars are somewhat larger than those we use for killed steel because the liquid steel is at a higher temperature and the total volume of blowholes formed is greater than the volume of the pipe formed by a killed steel.

As this bar is lowered into the molten metal, the latter, of course, solidifies about the bar, forming an envelope, V, W, X, Y, Figures 6 of definite thickness, and leaving a surrounding column of molten metal between it and the shell formed by the initial rimming action from the wall of the mold. This envelope forms as the bar is lowered into the metal and continues to grow rapidly for a certain period thereafter.

cause a rapid solidification of the metal in the "center and a rapid cooling of the remaining liquid from the higher temperatures of teeming down to or within a few degrees of the liquidus for the steel, thus producing at first an effect, and causing reactions to take place, like those produced when the rim about the ingot is formed. The rapid cooling, however, checks the gas forming reactions and prevents segregation of both metallic and nonmetallic components of the steel, with the result that all those components having low fusion points which tend to segregate on slow cooling are forced to remain in a finely dispersed state as this metal passes from the liquid to the solid state at an almost constant temperature.

The lowering 'of the insert bar also carries molten metal from the upper portion toward the bottom of the ingot and sets up currents differing in direction and intensity from those in ingots cast by the prior art. As the column of liquid metal solidifies, its heat of fusion is transmitted to the solidified column surrounding the bar inserted and causes the entire column of solidmetal to expand at a rate approximately equal to its contraction as it solidifies. At the same time this latent heat raises the temperature of the bar inserted to a welding heat which, with the pressure now being applied, is sufficient to cause a union between the bar and the metal solidified about it.

The result is an ingot having a rim comparable with that obtained in rimming steel produced by the prior art, but with a central portion free of cavities of all kinds, and of uniform composition, comparable with the best practice as shown by the following table of analysis of steels produced by the prior art and by means of our invention.

The following is a table comparing composition of a cross section of an ingot of rimmed steel as produced by the process of our invention with those produced by the best practices of the prior art. Test numbers stand for samples taken from the edge to the center of the ingot, Test No. 1 being at edge of each ingot.

Test

0 Mn P s 1 .07 .37 .010 .020 2 .00 .37 .010 .018 3 .07 .37 .014 .020 4 .13 .41 .015 .040 5 .14 .40 .019 .047 Ingot 1, rimming con- 6 .13 .40 .018 .046 trolled by insert 7 14. 41 018 045 s .13 .40 .020 .044 0 .14 .40 .010 .044 10 .13 .40 .018 .044 11 .13 .40 .014 .044 12 .13 .39 .015 .042 1 .07 .37 .012 .013 2 .00 .30 .012 .022 3 .11 .30 .010 .030 4 Ingot 2. nmmlng con- "9 by add'mg :li zit :St? 1822 mmum s -.13 .43 .018 .045 0 .14 .42 .018 .045 10 .14 .43 .015 .045 11 .14 .43 .018 .041 12 .11 .42 .015 .034 1 .00 .30 .017 .010 2 .00 .35 .010 .020 3 .10 .37 .010 .032 ,4 .12 .38 .010 .030 Ingot 3, rimming con- 5 .14 .42 .017 .044

trolled by furnace prac- 6 14 41 018 045 tice and teeming tem- 7 .13 .40 .019 .040

pcrature 8 13 40 019 04 "rim of solid steel formed within the The size of the bar to be inserted is calculated from the cross sectional area of the ingot and the specific heats of alpha iron, beta iron, gaa iron, and liquid iron and the thickness of the rim desired. Thus, the total heat that may be absorbed by the insert bar in raising its temperature. from atmospheric (temperature to the solidus point should equal the total heat that may be given up by the basin of metal enclosed by the ingot mold as indicated by the area outlined by the letters 2', s, t, u. in the diagram of Figure 6.

The use of our invention also yields other advantages not possible by any practices of the prior art of steel-making. Thus, the use of the insert causes the ingot to solidify in a. much shorter time than an ingot not treated by the process of our invention, making it practicable to strip the mold from the ingot and charge it into the soaking pits much sooner after pouring. The practice of our invention also lowers the heat required to bring the ingot to rolling temperature, since it can be stripped sooner and charged hotter; and since it eliminates completely the danger of rolling ingots with soft or mushyv centers, it shortens considerably the time it is necessary to hold the ingots in the soaking pits. So, it not only decreases the amount of discard from the top of the ingot, but also lowers the cost of heating the ingots for rolling.

The process of our invention has the added advantage that it is applied with safety, and no fumes of a poisonous or toxic nature that may be injurious to the health of the workman are given oi! as the insert bar is lowered into the ingot.

We claim:

. 1. A method for preventing the formation of pipe in ingots of killed steel, comprising teeming liquid steel into an ingot mold, permitting the steel to stand in the mold until a portion next to the mold has solidified, treating the top surface of the ingot to expose an area of liquid steel, cleaning a bar of steel to render it scale-free, and lowering through the exposed area of liquid the resulting cleaned steel bar having-a surface free of scale and other harmful surface defects and having a cross sectional area so proportioned tothat of the ingot that the bar does not reach a temperature above solidus range, thereby avoid- Q ing appreciable softening of the bar while causing metal to solidify around the bar but at welding temperature to weld thereto and preventing any appreciable remelting of the resulting solidifled metal.

ering through the top surface thereof the said steel bar which is free of scale and other surface defects and a cross sectional area so proportioned to that of the ingot that the bar does not reach a temperature sumciently high to become pasty while causing metal to solidify around the bar and to weld thereto and while preventing the resulting solidified metal from remelting.

3. A method for preventing the formation of a pipe in an ingot of semi-killed steel, comprising cleaning a steel bar to render it scale-free, teeming liquid steel into an ingot mold, permitting the steel to stand in the mold until a portion next to the mold has solidified, treating the top surface of the ingot to expose an area of liquid steel and lowering through the exposed area of liquid steel the said steel bar which is iree of scale and other surface defects and a cross sectional area so proportioned to the size of the ingot mold that the bar does not soften and lowers the temperature of the steel remaining liquid to a point between the liquidus and solidus temperatures of the steel while causing metal to solidify around the bar and to'weld thereto, the temperature of the steel remaining liquid being rendered insufiicient to cause any appreciable remelting of the said solidified metal, solidification of the remaining steel being accelerated thereby in an upward di-- rection at a rate greater than lateral solidification from the said rim.

4. A method of minimizing internal defects in ferrous metal ingots, which comprises filling an ingot mold with molten metal, covering the top surface of the molten metal in the mold with a material adapted to maintain the metal in liquid condition at and below the top surface of the metal, permitting the liquid metal to stand until the top surface thereof sinks to form a basin of a predetermined depth, removing the covering material from an area of the metal at the center of the bottom of this basin, and gradually lower ing into the liquid metal a clean solid bar of like metal along the central axis of the ingot, the said bar being of a size, and the speed of lowering at such a rate, that the displaced metal does not overflow the said basin formed by the sinking of the surface of the liquid metal.

5. A method of minimizing internal defects in steel ingots, which comprises filling an ingot mold with liquid steel, covering the top surface of the liquid steel with a material adapted to prevent the steel from freezing over this surface, permit- 1 ting the ingot to stand unti the top sinks to form 2. A method for preventing the formation of a I pipe in an ingot of semi-killed steel, comprising cleaning a steel bar to render it scale-free, teeming liquid steel into an ingot mold, permitting next'to the mold has solidified and, before a crust the steel to stand in the mold until a portion a basin equal in volume to more than half of the volume of the pipe cavities characteristic of the steel, removing the said material from the central area of the said basin, and slowly loweringalong the'central axis of the ingot a bar of steel, the volume of which exceeds one-half of the liquidto-solid contraction of the steel remaining liquid at the time of lowering the said bar.

6. A method of minimizing internal defects in 'ingots of fully killed steel, which comprises filling an ingot mold with the liquid steel, covering the top surface of the liquid steel'with a material adapted to prevent the top surface of the steel from freezing over, permitting the ingot to stand until its top surface sinks to form a basin having a volume of more than 1 /2 per cent of the volume of the ingot, removing the covering from the central area of the volume of the basin, and gradually lowering along the principal central plane of the ingot a clean piece of solid steel having a cross section similar in shape to that of the ingot, a length and width approaching i fied, which comprises forming the insert to required dimensions, attaching supporting means to the insert for enabling the insert to be supported in vertical position, heating the insert to a temperature between 400 F. and 600 F., immersing the insert while hot in a hot solution of sulphuric acid to remove scale from the insert,-

rinsing the insert in a hot dilute solution of hydrochloric acid, dipping the insert in a warm dilute solution of sodium cyanide and then in a concentrated solution of sodium cyanide containing from about 0.2 pound to about 0.4 pound of sodium cyanide per gallon, allowing the insert to dry, and dipping the insert in a mixture of organic and petroleum oils, at least one of the organic oils of the mixture being a reactant for sodium cyanide.

8. A method of preparing steel inserts for use in the treatment of liquid steel ingots for mini- .mizing internal defects in the ingot when solidified, which comprises forming the insert to required dimensions, immersing the insert in hot sulphuric acid solution to remove scale, treating the insert in a molten bath of sodium cyanide and sodium carbonate to decompose ferrous sulphate, eliminate hydrogen and slightly nitride and carburize the surface, allowing the insert to cool, removing at least the major portion of adhering sodium cyanide, dipping the insert in hot water, and coating the insert with a mixture of organic and petroleum oils, at least one of the organic oils of the mixture being reactive with sodium cyanide.

9. A method for producing ingots, which comprises casting molten metal in an ingot mold, and lowering therein prior to formation of acrust thereover a clean, scale-free metal bar having a specific gravity greater than the liquid metal in the mold, and a cross section of such an area that the inserted bar remains solid in the molten metal while producing solidification of the metal around the bar and while absorbing sufiicient heat from the cast metal to cause the solidified metal to weld to the bar while avoiding any substantial remelting of the said solidified metal during solidification of the remaining metal in the mold.

10. A method for producing ingots, which com-- prises casting liquidmetal in a mold, allowing the metal to stand in the mold until a shell of the metal solidifies adjacent to the mold, inserting into the molten metal in the mold a clean solid bar of metal as an insert in the molten metal, the said bar being proportioned as to size and temperature relative to the molten metal in the mold so that as the bar is inserted in the mold molten metal therein solidifies upon the said bar and welds thereto while avoiding at all times any melting of the bar and any remelting of the said welded metal during solidification of the remaining molten metal thereon, and inserting the said bar being inserted into the. metal in the mold prior to a crust forming on the top surface of the said metal and along approximately the longitudinal axis of the mold, as well as being inserted at a rate preventing appreciable displacement of level of the metal in the mold, and allowing the metal in the mold to solidify completely.

11. A method of casting and treating steel ingots to prevent the formation of pipe and to overcome other internal defects, which comprises shaping an insert bar of steel to desired dimensions, immersing the shaped bar into a molten bath composed of sodium carbonate between 7 and 8 parts, and sodium cyanide between 2 and 3 parts, maintaining the molten bath at a temperature above 1400 F., permitting the immersed bar to remain in the molten bath until all scale and oxide are reduced, transferring the bar to a I trough or' box containing a salt mixture which includes sodium cyanide, permitting the bar to cool therein to a temperature slightly above that at,which the salt mixture solidifies, removing the bar and permitting it to cool to a temperature below 425 F., detaching the adhering excess salt prior to lowering it into an ingot being cast, filling an ingot mold with liquid steel, and lowering the thus-prepared bar of steel vertically into the liquid steel along the central axis of the ingot mold before a crust has formed on the top surface of the ingot, the bar being lowered at a rate favoring solidification of the liquid steel around the bar as it moves into the steel.

12. A method of casting and treating steel ingots to prevent the formation of pipes and to overcome other internal defects, which comprises 'shaping an insert bar to desired dimensions,

immersing the shaped bar into a molten bath composed of sodium carbonate, between 7 and 8 parts, and sodium cyanide between 2 and 3 parts, maintaining the molten bath at a temperature above 1400 F., permitting the immersed bar to remain in the molten bath until all scale and oxide are reduced, transferring the bar to a trough or box containing a salt mixture which includes sodium cyanide, permitting the bar to cool therein toa temperature below 425 F., re-

moving the bar from the solidified salt mixture, washing off adhering salt in excess of the amount desired, drying the bar,at least some ,of the salt being permitted to remain on the bar, filling an ingot mold with liquid steel, and lowering the thus-prepared steel bar vertically into the liquid steel along the central axis of the ingot mold before a crust has formed on the top surface of the ingot, the bar being lowered at a rate favoring solidification of liquid steel from the molten ingot on the bar as the bar moves into the steel.

13. In the prevention of internal defects in steel ingots by inserting a steel bar in molten steel contained in an ingot mold, the improvements which consist in shaping the bar to the desired dimensions, heating the prepared bar to a temperature above 212 F., immersing the heated barinto a solution of an acid .to remove scale, permitting the bar to dry while protecting the bar from oxidizing, and lowering the nonoxidized bar into the ingot of liquid steel vertically along the central axis of the ingot mold before a crust has formed on the top surface of the ingot, the bar having a cross-sectional area and being lowered at a rate to favor solidification of the liquid steel around the bar as it moves into thesteel, while preventing the bar from reaching a temperature sufficiently high to become pasty so that the solidified steel welds to the bar and is prevented from remelting.

14. In the prevention of internal defects in steel ingots by inserting a steel bar in molten steel contained in an ingot mold, the improvements which consist in shaping the bar to the forms on the top surface of the molten steel in the mold, lowering the thus-prepared bar slowly into the liquid steel along the central axis of the ingot at a rate which does not cause appreciable displacement of the liquid steel from its original level, and permitting the whole to solidify.

15. In the prevention of internal defects in steel ingots by inserting a steel bar in molten steel contained in an ingot mold, the improvements which consist in shaping the bar to the desired dimensions, heating the prepared bar to a temperature of above 212 F., immersing the heated bar into a solution of an acid to remove scale, immersing the bar in a very dilute solution of a non-oxidizing acid to remove solution adhering from the prior treatment, then into a dilute solution of an alkali cyanide containing less than it) grams per liter and into a concentrated solution of an alkali cyanide containing more than 30 grams of the cyanide per liter, permitting the bar to dry, and lowering the thus-treated bar vertically into' the liquid steel along the central axis of the ingot mold while the surface of the again immersing the bar in a dilute solution of acid, then into a dilute solution of an alkali cyanide containing less than 10 grams per liter and into a concentrated solution of an alkali cyanide containing more than 30 grams of the cyanide per liter, permitting the lebar to dry, and

lowering the thus-treated bar vertically into the liquid steel along the central axis of the ingot mold while the surface of the ingot is'in the liquid state, the area of the bar being proportioned to that of the ingot so as to cause the liquid steel to freeze around the bar as the bar passes into the ingot without melting the bar.

' 17'. In the prevention of internal defects in steel ingots by inserting a steel bar in molten steel contained in an ingot mold, the improvements which consist in cleaning the bar with a cyanide bath,

ingot is in the liquid state, the area of the bar being proportioned to that of the ingot so as to cause the liquid steel to freeze around the bar as the bar passes into the ingot without melting the bar;

16. In the prevention of internal defects in steel ingots by inserting a steel bar in molten steel contained in an ingot mold, the improve- =ments which consist in shaping the bar to the desired dimensions, heating the prepared bar to a temperature above 212 F., immersing the heated bar into a solution of an acid to remove scale, immersing the harm a very dilute solution of an acid to remove solution adhering from the prior treatment, then washing it with an alkali hydroxide solution to remove smut,

permitting the bar to dry, coating the bar with an organic oil mixture that will preserve and fix the cyanide on the surface and protect the bar from corrosion, permitting the excess oil to drain from the bar, and, before a crust has formed over the surface of the steel, lowering through the top surface the thus-prepared steel bar, which has a cross-sectional area so proportioned to that of the ingot that the bar does not reach a tempera= ture sufllciently high to become pasty while causing metal to solidify around the bar and to weld thereto and while preventing the resulting solidified metal from remelting.

18. In the prevention of internal defects in steel ingots by inserting a steel bar in molten steel contained in an ingot mold, the improvements which consist in shaping the bar to the desired dimensions, heating the prepared bar to a temperature above 212 F., immersing the heated bar into a solution of acid to remove scale, coating the bar with a thin metallic corrosionresisting coating to preserve it from corrosion, and inserting the thus-prepared bar into the molten steel prior to formation of a crust over the top surface of the steel, so that the long axis of the bar coincides with the long axis of the mold.

CHARLES B. FRANCIS. PAUL B. GUYER. 

